1. Field of the Invention
The present invention relates to an SOI (silicon-on-insulator) semiconductor device and a method of producing same. More particularly, the present invention relates to reducing warpage of an SOI semiconductor device.
2. Related Art
It is known to form an isolation trench in an SOI semiconductor device, bury this trench in polycrystalline silicon, and isolate between various elements. For example, such a structure and method is discussed in Japanese Patent Application Laid-open No. 5-109882.
In order to eliminate differences in levels occurring in the isolation trench when forming the isolation trench, an oxide film is formed on the semiconductor substrate. In addition, a silicon nitride film is formed above the trench before forming the isolation trench. Accordingly, oxide film for the formation of the isolation trench is required. Trench formation and oxidation of the trench inner wall surfaces and polycrystalline silicon burying are performed sequentially. The oxide film for isolation trench formation that remains on the substrate surface is removed with reactive ion etching (RIE).
Currently, the silicon nitride film functions such that oxide film formed on the trench inner walls is not simultaneously removed when the oxide film used for isolation trench formation is removed. Thus, the occurrence of differences between the levels in the isolation trench portion is prevented.
However, when the above-described semiconductor device is actually formed, the silicon nitride film is also deposited on the rear surface of the substrate. Although this nitride film deposited on the rear surface can be expected to prevent the penetration of undesirable contaminants from the substrate's rear surface side, the present inventors have found that the SOI substrate is warped by the internal stress of the nitride film itself when a trench is formed on the SOI substrate. This warpage of the substrate not only causes undesirable crystalline defects in a region where semiconductor elements are formed, but also hinders good formation of uniform elements within the wafer during element formation.